Method of increasing the initial modulus and reducing the orientation angle of undrawn poly (para-benzamide) fibers

ABSTRACT

High molecular weight polymers consisting essentially of recurring units of the formula   ARE USEFUL FOR THE PRODUCTION OF FIBERS HAVING A HIGH INITIAL MODULUS. The initial modulus is increased and the orientation angle is reduced in the undrawn fibers by heating the fibers at a temperature of at least 350*C while under tension, or while relaxed.

United States Patent [1 1 Kwolek June 10, 1975 METHOD OF INCREASING THEINITIAL MODULUS AND REDUCING THE ORIENTATION ANGLE OF UNDRAWN POLY(PARA-BENZAMIDE) FIBERS [75] Inventor: Stephanie Louise Kwolek,

Wilmington. Del.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington. Del.

[22] Filed: Feb. 9, I973 [21] Appl. No.3 331.322

Related U.S. Application Data [63] Continuation-impart of Ser. No.30,089, April 20, 1970. abandoned. which is a continuation of Ser. No.644.851. June 9. 1967, abandoned. which is a continuation-in-part ofSer. No. 556.934. June 13. 1966. abandoned.

[52] US. Cl. 264/342 RE; 264/184; 264/205;

264/346 [51] Int. Cl. B290 25/00 [58] Field of Search 264/184. 205. 235.346.

264/210 F. 290 N, 342 RE; 161/172 [56] References Cited UNITED STATESPATENTS 3.414.645 12/1968 Morgan, Jr. 264/210 F 3,595,951 7/1971 Logullo264/211 Primary E.\'aminer-Robert F. White Assistant Examiner-James B.Lowe [57] ABSTRACT High molecular weight polymers consisting essentiallyof recurring units of the formula are useful for the production offibers having a high initial modulus. The initial modulus is increasedand the orientation angle is reduced in the undrawn fibers by heatingthe fibers at a temperature of at least 350C while under tension. orwhile relaxed.

1 Claim, 1 Drawing Figure RELATIVE INTENSITY 0F X-RAY DIFFRACTION METHODOF INCREASING THE INITIAL MODULUS AND REDUCING THE ORIENTATION ANGLE OFUNDRAWN POLY (PARA-BENZAMIDE) FIBERS CROSS-REFERENCE TO RELATEDAPPLICATIONS This application is a continuation-in-part of my copendingapplication Ser. No. 30,089, filed Apr. 20, 1970, which in turn is acontinuation of my application Ser. No. 644,851, filed June 9, 1967, nowabandoned which in turn is a continuation-in-part of my application Ser.No. 556,934, filed June 13, 1966, now abandoned.

DETAILED DESCRIPTION In accordance with this invention, there isprovided a process for treating high molecular weight substantiallyhomopolymeric poly(p-benzamide) fibers consisting essentially ofrecurring units of the formula I! O n In the inherent viscosity range offrom about 0.8 to about 2.5 (measured as described hereinafter) thispolymer is useful for the production of fibers. At values of inherentviscosity as low as about 0.7, it is useful for the production of films,fibrids, and coatings. These uses require the polymer to bepreliminarily in the form of a dope.

The most stable dopes to be used for extrusion of the homopolyamidereferred to above into filaments contain, on a weight basis, between 4and 30% of polymer, preferably 5 to from 3 to 22% lithium chloride(LiCl), and the remainder tetramethylurea (TMU). At least 0.5 mol ofLiCl should be present per repeating unit of polymer. However, thepresence of LiCl is not necessary if the dope is used within areasonable period after preparation. Thus, to assure that the dope is inproper condition for dryor wet-spinning, either the polymer is preparedin TMU or in TMU-LiCl optionally followed by complete or partialneutralization of the by-product acid, and spun directly (coupledprocess). It is not necessary that the by-product acid be neutralized,except that it is found to be corrosive to the spinning equipment. In analternate procedure, the polymer is first prepared and isolated, thencombined with TMU-LiCl all as indicated below.

The essentially homopolymeric poly(p-benzamide) in this invention mayreadily be obtained by certain polymerization techniques from suitablemonomers. For example, it may be obtained by the low temperaturesolution polymerization of p-aminobenzoyl halide salts of the formulaFormula I.

H3N+ Formula II wherein X, represents a member selected from the groupconsisting of arylsulfonate, alkylsulfonate, acid sulfonate,p-aminobenzoyl chloride toluenesulfonate,

p-aminobenzoyl bromide ethanesulfonate, and paminobenzoyl chloridesulfate. The preferred paminobenzoyl chloride hydrochloride may beprepared solution of pin, high yield from an etherealthionylaminobenzoyl chloride by the general procedure of Graf andLanger, .I. prakt. Chem. 148, 161 (1937) under anhydrous conditions. Thedrying and anhydrous storage of this monomer are preferably performedunder room temperature conditions because of the tendency for thecompound to polymerize at higher temperatures.

POLYMERIZATION CONDITIONS The low temperature, i.e., under 60C. andpreferably from 0-20C., solution polymerizations which pro vide thepolyamide useful in this invention preferably employ a solvent selectedfrom the group consisting of TMU, hexamethylphosphoramide, N,N-dimethylacetamide, and N-methylpyrrolidone. Other useful polymerizationmedia are N-methylpiperidone, N,N-dimethyl ethylene urea,N,N,N',N-tetramethylmalonamide, N-methylcaprolactam, N-acetylpyrrolidine, N,N-diethylacetamide, N- ethylpyrrolidone,N,N-dimethylpropionamide, N,N-

dimethylbutyramide and N,N-dimethylisobutyramide.

The above-mentioned polymerizations may be carried out by dissolving thedesired monomer in the amide solvent and vigorously stirring theresulting solution, externally cooled, until it becomes very viscous.The polyamide may then be isolated by the addition of water.Alternatively, the monomer may first be slurried in a small quantity ofan inert organic liquid prior to the addition of the amide solvent. In avariation of the former method, the solvent maybe frozen and mixed,while frozen, with the desired monomer. The solvent is permitted to thawand the resulting slush stirred until a gel-like mass forms. A suitablechain-terminating agent may be used in these reractions in order tolimit the molecular weight of the polymeric product. For the attainmentof the highest molecular weights, these polymerizations are performedunder strictly anhydrous conditions. The reaction vessel and auxiliaryequipment, solvents, and reactants are'carefully dried prior to use andthe reaction vessel is continuously swept with a stream of dry, inertgas, e.g., nitrogen, during the polymerization.

One such polymerization may be accomplished by first adding, withstirring, a quantity of an anhydrous organic liquid, such astetrahydrofuran, dioxane, benzene, or acetonitrile, to a quantity of thedesired monomer in the gasswept polymerization apparatus. This liquidalso contains the calculated amount of the desired chain-terminatingagent, e.g., benzoyl chloride, whenever this agent is to be used. Theresulting mixture is stirred at an increased rate and a relatively largevolume of anhydrous amide solvent, e.g., TMU, N,N- dimethylacetamide,hexamethylphosphoramide, or N- methylpyrrolidone, is then rapidly addedto the flask.

The resulting solution, extenally cooled, is stirred continuously untilthere is a substantial increase in the viscosity of the composition. Thelatter may, if desired, stand overnight or longer at room temperature.When the polymer is to be isolated in bulk form, the polymerizationmixture is combined with water in a suitable blender and then isconverted to a fine powder. The powdered polymer, after being washedwith both water and alcohol, is dried overnight in a vacuum oven atabout 8090C. before being stored or dissolved for subsequent processing.

As indicated above, chain terminators may be used in thesepolymerizations. By assisting in the control of v the molecular weightof the polyamide, the use of chain terminators contributes to the easeby which subsequent dissolution of the polymer occurs and enhances thestability of the polymer dope for application in the coupledpolymerization spinning process. Among the suitable chain terminatorsare monofunctional compounds which can react with the acid chloride endsof these polyamides such as ammonia, monoamines (e.g., methylamine,dimethylamine, ethylamine, butylamine, dibutylamine, cyclohexylamine,aniline, etc.), compounds containing a single amide-forming group, suchas N,N-diethylethylenediamine, hydroxylic compounds such a methylalcohol, ethyl alcohol, isopropyl alcohol, phenol, water, etc., andmonofunctional compounds which can react with the amine ends of thepolyamides such as other acid chlorides (e.g., acetyl chloride), acidanhydrides (e.g., acetic anhydride, phthalic anhyrdide, etc.), andisocyanates (e.g., phenyl isocyanate, m-tolyl isocyanate, ethylisocyanate, etc.).

All useful terminators are especially effective and uniformlydistributed if added at the beginning of the polymerization or prior tothe addition of any acidneutralizing agent (e.g., lithium hydroxide).

The essentially homopolymeric poly(p-benzamide) possesses a peak heightratio of below 0.86 and, moreover, no sediment is seen in the tube whenthe polymer is subjected to the sedimentation test, all-as describedbelow. It has been found that polymer of inherent viscosity 0.80 andmeeting these two requirements can be spun into yarns having anextremely high modulus and a low orientation angle. It will beunderstood, however, that the peak height ratio as measured on polymerthat has been spun or heated at elevated temperatures may exceed 0.86.Sedimentation properties may also change on heating or spinning.

DOPE PREPARATION The polyamide which has been prepared by the previouslydescribed methods and which has been isolated from the polymerpreparation system are then incorporated into dopes for spinning, etc.One such method is as follows: a mixture of homopolyamide, TMU, andlithium chloride in proportions earlier defined is placed in a suitablevessel equipped for stirring. The mixture is stirred and heated at aboutl30-l50C. for at least 1 hour. While the stirred mixture is maintainedat this temperature, it generally becomes an extremely viscous,gelatinous mass completely unsuitable for spinning. This material isthen cooled to about C. or below in a bath of solid carbon dioxide, orby other spinnable dope.

The amount of heating and cooling required to form by this method a dopewith the flow characteristics needed for smooth spinning varies with theinherent I or even longer and the mixture is useful as a dope that canbe spun or cast. Gelling may begin to occur in from about 0.5 to 2 hoursreaction time, depending in part at least upon the degree ofpolymerization attained. The stability of such dopes may be extended toperiods of many days by the addition of chain-terminating agentsdescribed earlier. A directly extrudable dope may be obtained wherepolymerization is continued in TMU for a time in excessof about 0.5 houror more by adding a quantity of lithium chloride to the TMU medium priorto the polymerization or by adding to the half hour-old reaction systema quantity (up to 2 equivalents of lithium per mole of monomer chargedwhen an acid chloride hydrochloride is employed) of an inorganic salt orsalt-forming reagent such as lithium chloride, lithium acetate, lithiumhydroxide, lithium carbonate, or lithium oxide; in addition, externalheat may be subsequently applied to the contents of the reaction vesselto assist in forming or maintaining the extrudable dope. The above-citedbasic materials each react with the hydrogen chloride formed during thepolymerization to generate lithium chloride in situ. It is preferredthat lithium hydroxide, lithium oxide and like bases be used in amountsnot in excess of that required to new tralize the hydrogen chloride orother acids formed in the reaction. In spinning those TMU dopesdescribed above, spinnerets of platinum-gold construction andreservoirs, filters, conduits, and the like, prepared from, for example,corrosion-resistant stainless steel, are particularly suitable. Metalscoated with Teflon polyfluorocarbon and glass-lined equipment, as wellas acid-, heat-, and solvent-resistant plastic parts may be used.

SHAPED ARTICLES AND THEIR PREPARATION Conventional wetand dry-spinningtechniques and equipment can be used to prepare the polyamide filamentsfrom the previously described dopes. In wet spinning, an appropriatelyprepared TMU (or other suitable solvent) dope of the polyamide, whosetemperature may vary from room temperature to about C is extruded into asuitable coagulating bath, e.g., a water bath maintained at 6590C. Otheruseful coagulants include ethylene glycol, glycerol, mixtures of TMU andwater, mixtures of alcohol and water, and aqueous salt baths. These arepreferably maintained at a temperature of 40-45C. or above. Formation ofgood fibers (i.e., those with enhanced tensile properties) is assistedby keeping the filaments taut while they are in the coagulating bath.This may be accomplished, for example, by passing the filaments aroundguides placed in the coagulating bath.

- whereby the TMU is evaporated.

After being formed, the filaments are passed over a finish-applicationroll and wound up on bobbins at high speeds. They can be readilyback-wound. Development of maximum levels of filament and yarnproperties is assisted by soaking the bobbins in water or in mixtures ofwater and water-miscible inert organic liquids (e.g., TMU, DMAc,acetone, ethyl alcohol, glycerol) to remove residual solvent and salt.The removal of salt and any residual solvent may also be accomplished bypassing the yarn through aqueous baths on the run, by flushing thebobbins with water as the yarn is formed, and by washing or soakingskeins, rather than bobbins, or yarn. The yarn is strengthened bywashing with even a minor amount of water.

The fibers possess high tenacity and a very high initial modulus, i.e.,above 200 gpd. and often exceeding 300 gpd., which is necessary for manyreinforced plastic applications. They are crystalline and possess anorientation angle of less than about 35. In general, as shown in theexamples which follow, homopolymeric poly(pbenzamide) filaments preparedand treated as described above, possess these unusual and unanticipatedtensile properties without being drawn. The freshly extruded filamentsare usually of low void content. Use of spin Stretch factors (definedbelow) approaching one in dry spinning or, on occasion, in wet spinningwith such polymers will yield as-spun fibers having an orientation angleof above 35 and a modulus below 200. In that event, the fiber may beheated taut at about 400C. for about 2-5 seconds in nitrogen to bringthe orientation angle down and the modulus up.

As used herein the term as-spun" or undrawn describes the filamentcondition at the wind-up or first roll following extrusion. Spinstretch, which is not considered as draw, may occur in the zonepreceding the first roll depending on the yarn velocity at the firstroll as compared to the velocity of the dope as it passes through thespinneret holes. The yarn may be drawn after it leaves the first roll.

Heat treatments of the as-spum filamements under tension or with only aslight amount of drawing produce a significant increase in theirtenacity and modu-- lus values. The tensile properties of thesefilaments can also be enhanced by subjecting the unknown fibers to aheat treatment in the relaxed state. Hot air ovens, hot pins, hot slots,hot plates and liquid heating baths are useful for suchtreatments.Heating is generally carried out above 350C. while drawing said fibersless than about it will be understood that the selection of heating timeand temperature will be such as to avoid undue polymer degradation.

The chemical and thermal stabilities of filaments and yarns preared frompoly(p-benzamide) by the processes of this invenion are excellent. Thefibers retain their tensile properties after being heated at the boilfor 0.5 hour in aqueous hydrochloric acid (1%) and caustic (1%)silutions. The fibers are essentially unaffected after being soaked forone hour at 60C. in commercially-used dry cleaning solvents such asPerclene" perchlorethylene and Triclene trichlorethylene. The fibersdisplay excellent retention of tensile properties during and afterheating in air at 300C. for a prolonged period. The fibers areself-extinguishing when removed from an open flame.

It will be understood that the usual additives such as dyes, fillers, UVstabilizers, antioxidants, etc. can be incorporated in with the polymerfor the purposes intended prior to fiber preparation.

MEASUREMENTS AND TESTS Orientation Angle: The orientation angle of thefiber is determined by the general method described in Krimm andTobolsky, Textile Research Journal, Vol. 21, pp. 805-22 (1951 A wideangle X-ray diffraction pattern (transmission pattern) of the fiber ismade, using nickle-filtered Cu radiation, a fiber-sample thickness of 20mils (0.05 cm.), a sample-to-film distance of 5 cm., and an exposuretime of 45 minutes. The arc length in degrees at the half-maximumintensity of the first equatorial diffraction spot, which is located at203, 20, is measured and taken as the orientation angle of the sample.Since the intensity trace is an essentially Gaussian curve and themeasurement is made at half-maximum intensity, the physical meaning ofthe orientation angle given by the determination is that approximately77% of the crystallities are aligned within this angle about the fiberaxis.

Peak Height Ratio: A measure of the relative intensity of the two 'majorequatorial diffraction peaks is given by the peak height ratio (PHR). Asuitable method for determining the PHR involves the use of a reflectiontechnique to record the intensity trace of the X-ray diffraction patternwith an X-ray diffractometer. Approximately 0.5 gram of waterandTMU-free polymer is pressed into a Phillips sample holder under anapplied pressure of 3,125 lb./in. (219.7 X 10 g/cm. Usingnickle-filtered Cu radiation, a Philips diffractometer with O.5 slits,and a pulse height analyzer, a trace of intensity is recorded from 6 to40, 20, at a scanning speed of 1, 26, per minute, a chart speed of 1inch per minute (2.54 cm./min.), and a time constant of 2; 20 being theangle between the undiffracted beam and the diffracted beam. The fullscale deflection of the recorder is set so that the peak with maximumintensity is at least of the scale, which is a linear scale. Tocalculate the PHR, a base line is first established on thediffractometer scan by drawing a straight line between the points on thecurve at 8 and 38, 20. Vertical lines (at constant 26 values) are drawnfrom the peaks in the vicinity of 203 and 23.4", 20, to the base line,and the height of the peaks, in chart divisions, above the base line isascertained. The PHR is then calculated from the equation PHR A/B whereA height of the peak, approximately located at 20.3, 20, above the baseline in chart divisions, B

SEDIMENTATION TEST Polymer powder (0.10 g.), as prepared, is dried,comminuted to pass through a 20-mesh screen, and

placed in a dry test tube. To this added 10.0 ml. of a solution oflithium chloride (6.9% by weight) in tetramethylurea. The tube isstoppered and its contents subjected to mechanical agitation (the tubeis rotated at 1 10 rpm about a diametrical axis through its mid-pointfor 24 hours at 21C.). The tube is then allowed to stand-upright for afurther 24 hours. After this time no polymer residue lies settled on thebottom of the tube.

SPIN STRETCH FACTOR merization, 1.20 ml. of benzoyl chloride (distilled)is added to the above-mentioned tetrahydrofuran.

where Vel ..of dope through spinneret Rate of pumping (cu. ft./min.l No.of spinneret holes x cross-sectional area of one hole (sq. ft.)

INl-IERENT VISCOSITY Inherent viscosity (ninh) is defined by thefollowing equation:

ninh 1n ('qrel)/C wherein (nrel) represents the relative viscosity and(C) represents a concentration of 0.5 gram of the polymer in 100 ml. ofsolution. The relative viscosity (nrel) is determined by dividing theflow time in a capillary viscometer of a dilute solution of the polymerby the flow time for the pure solvent. The dilute solutions used hereinfor determining (nrel) are of the concentration expressed by (C), above;flow times are determined at 30C., using concentrated (95-98%) sulfuricacid as a solvent.

Fiber properties of tenacity, elongation, and initial modulus are codedas T/E/Mi and are reported in their conventional units. Denier is codedas Den. The boiling off treatment of fibers prior to physical testingconsists of boiling the fibers 30 minutes in 0.1% aqueous sodium laurylsulfate, rinsing, drying at 40C. for 1 hour, and conditioning at 21C.and 65% r.h. for 16 hours.

Tensile properties were determined on yarn samples which measured oneinch (2.54 cm.) in length between the jaws of an Instron tester (productof the Instron Engineering Corp., Canton, Mass.) and which are subjectedtherein to a load sufficient to cause elongation to occur at the rate of10% per minute measured at 21C. and 65% r.h.

The following nonlimiting examples are illustrative of the practice ofthe invention.

EXAMPLE I Polymer Preparation: A two-liter resin-making kettle equippedwith a stirrer, nitrogen-inlet tube and calcium chloride drying tube isflamed with a Bunsen burner and simultaneously flushed with nitrogen.The kettle is sealed and placed in a dry-box, i.e., a chamber maintainedunder anhydrouos conditions. Hexamethylphosphoramide (520 ml., distilledfrom calcium hydride through a spinning band column at reduced pressureand stored over calcium hydride) is filtered in the drybox into aErlenmeyer flask which is then sealed and cooled in ice. Tetrahydrofuran(75 ml., distilled and stored over sodium metal, water content less than0.000l%) is filtered in the dry-box into an Erlenmeyer flask which isthen sealed and cooled in ice. p- Aminobenzoyl chloride hydrochloride(124.0 g., 0.646 mole) is weighed out in the dry-box and transferred tothe resin-kettle. The kettle is removed from the dry- 1 box, reconnectedwith the stirring motor and nitrogen The benzoylchloride-tetrahydrofuran solution is poured, with moderate stirring,into the .paminobenzoyl chloride hydrochloride and the mixture isstirred for about 1 minute. The stirring rate is increased and thehexamethylphosphoramide is rapidly added. The resulting mixture isstirred for about 1 hour while being cooled in an ice bath. The mixturegradually gels as a result of this treatment. The cooling bath isremoved and the polymeric mass is allowed to stand overnight at roomtemperature. The solid gel is then combined with water and stirred athigh speeds in a gallon-size (3.785 liter) blender wherein it isconverted to a fine, white powder. The polymer is washed 3 times withwater and once with alcohol by means of stirring in a blender andfiltration on a sintered-glass mediumpore Buchner funnel. The polymer isdried overnight in a vacuum oven at 90C. The yield of poly(pbenzamide)is 92.3% (ninh 1.35). The polymer had a peak height ratio of 0.78. Whensubjectedto the sedimentation test, no solid residue remained at thebottom of the tube.

Dope Preparation: Into a 700 ml. bottle equipped with an air-drivenstirrer are placed 20 g. of the polymer and 180 g. of TMU/lithiumchloride solution containing 6.5% by weight of the salt. The resultingmixture is stirred and 'heated to 150C. by means of an oil bath. Thereis obtained an extremely viscous gelatinous mass. This mixture is cooledin solid carbon dioxide for 1 hour. the mixture is then heated at 150C.for 4 hours with stirring, to procude a fluid, somewhat gelatinous hazydope. The latter is cooled for 1 hour in solid carbon dioxide. Themixture is then stirred and heated for 4 hours at a temperataure of C.to produce a readily-spinnable haze dope which is subsequently cooled insolid carbon dioxide for 1 hour. This smooth, hazy dope flows slowly atroom temperature and reflects light upon being stirred.

Fiber Preparation by Dry Spinning: The dope prepared as above is heatedto 130C. and extruded at the rate of about 0.9 ml./min., under apressure of 70 lb./ir1. (4,921 g.cm. through a heated (l40144C.)protrusion-type spinneret having 4 holes of 0.004 inch (0.01 cm.)diameter and a capillary length of 0.008 inch (0.02 cm.), into a dryingcolumn'whose wallsare I kept within the range of 202210C. The column isswept with a cocurrent flow (5 ft. /min.; 0.142 m. /min.) of drynitrogen which enters the column at 265-270C. The emerging filaments,each of approximately 2 denier and having an oval cross-section, arepassed over a small guide roll bearing a finish solution and are woundup on a-bobbin at the rate of about 200 yd./min. (183 m./min.). Thisconstitutes a spin stretch factor of 6.58. The filaments do not stickand'are readily back-wound. These opaque exturded filaments becomelustrous white upon being soaked in changes of water (25C.) to removeresidual solvent and salt. The inherent viscosity of the polymer in thefilaments is 1.32. The water-leached, air-dried (70F. 65(l93)% r.h.)filaments exhibit crystallinity and an orientation angle of 21. A yarnprepared from these filaments exhibits the following T/E/Mi/Den. values(32 filaments; non-boiled-off): 6.02/2.l7/431/58.5. Filaments that havebeen boiled off display the following T/E/Mi/Den. values:4.75/l.38/429/l.72.

Heat Treatment of Fibers: The filaments or yarn prepared as above arepassed taut over a 3-inch (7.62 cm.) plate maintained at 438C. in asingle stage operation so as to increase their length by O-17r.Residence time over the hot plate was about seconds. The resultingfibers exhibit crystallinity and have an orientation angle of 13.Filaments have the following T/E/Mi/Den. properties (boiled off fiber):7.66/l.2/599/1.87.

Other filaments prepared as above were subjected to heat treatments inboth the relaxed and taut states. It was noted that the tensileproperties of the filaments were improved.

The following Table l summarized improvements obtained in the tensileproperties of water-leached, airdried undrawn poly(p-benzamide) fibersprepared similarly but not exactly as above. The fibers are given theindicated heat treatments in both the relaxed and taut stages for a 1hour period. Contrasting data is shown for a control sample. All valuesshown are for boiling off filaments and are obtained after the filamentsare returned to room conditions (70F., 65% r.h.).

TABLE 1 The above-described dope is dry-spun under the followingconditions: spinneret adapter temperature. 120C.; pressure on dope 100psi (7,031 g./cm. spinneret, 3 holes of 0.004 inch (0.01 cm.) diameter,each; spinneret temperature. 135140C.; column-wall temperature,195203C.; wind-up speed, 200 yd./min. (183 m./min.). the speed stretchfactor was 6.13. The yarn on bobbins is soaked in repeated changes ofwater at room temperature until essentially free of TMUv and lithiumchloride.

The T/E/Mi/Den. values of the washed and boiled-off fiber are7.16/2.l6/486/2.80, respectively. The fibers are crystalline and have anorientation angle of 16.

After passing the washed, dry fiber over a hot plate at 43 8C., theT/E/Mi/Den. values for a boiled-off sample of filaments are10.7/1.7/695/2.82, respectively. The filaments are highly crystallineand exhibit an orientation angle of 12.

EXAMPLE Ill Into a 2-liter resin kettle are placed 153.6 g. (0.8 mole)of p-aminobenzoyl chloride hydrochloride with stirring under nitrogen. A2% solution of lithium chloride in distilled TMU is prepared, heated at60C. and topped under vacuum to remove any water which might be present.About 800 g. of this solution are added rapidly to the monomer powder inthe resin kettle at 30C. while stirring. After about three-fourths of anhour, the first of three 4 ml. additions of diethylamine is made to stopthe polymerization. The second 4 ml. are added 5 minutes later and thefinal 4 ml. are added 30 minutes after that. About 70 g. (0.946 mole) oflithium carbonate are added 18 minutes later. The

Post-treatment Tensile Properties Observed Treatment Relaxed Fiber TautFiber Sample Conditions T B Mi T E Mi A 200C. hot air oven 6.88 1.75 4767.34 1.92 473 B 250C. hot air oven 7.38 1.67 491 7.45 1.72 456 Cl98210C. glycerol bath 6.79 1.79 457 6.17 1.62 443 D 235-268C.Silicone-550 6.61 1.48 506 7.50 1.74 503 oil bath E Control T/F/Mi:5.85/1 .69/426 Designation for a fluid. heat-stable silicone product ofthe Dow-Corning Corporation.

EXAMPLE I] This example illustrates the preparation of thepoly(p-benzamide) fibers of the invention wherein a coupled process ofpolymer production and filament spinning is employed. It will be notedthat the fiber properties are significantly enhanced after heattreatment.

In a 250 ml. round bottom flask (dried by flaming, filled with drynitrogen, equipped with a stirrer, drying tube, and nitrogen inlet, andimmersed in an ice-water bath) are combined 1 1.5 g. of p-aminobenzoylchloride hydrochloride and 61 ml. of cold TMU. Immediately solutionresults. The mixture is stirred for 2 hours at approximately 0C. and for16 hours at 26C. During this time the polymer separates as a swollenprecipitate. Lithium hydroxide (2.87 g.) is added as an anhydrous powderand stirred in. There is considerable heat of neutralization and shortlythereafter a nearly clear, viscous dope of polymer containing now LiClresults, which at l00120C., has the required consistency for faciledry-spinning. (The inherent viscosity of an isolated polymer sample is1.12. It has a peak height ratio of 0.73 and passes the sedimentationtest.)

resulting viscoussmix is then heated in an oil bath at l 15-120C.,diluted with 150 m1. of TMU and stirred under vacuum to distill offwater formed in the neutralization and excess solvent. F inal polymerconcentration is about 9%.

One portion of the mix is diluted in dimethylformamide/lithium chloride/5 and coagulated in water. The precipitated polymer is washed indistilled water three times and finally in acetone. It was then dried at60C. under vacuum. It has an inherent viscosity of 0.97, a peak heightratio of 0.80, and when subjected to the sedimentation test, leaves nosolid polymer residue at the bottom of the tube.

Fiber Preparation by Wet Spinning: The 9% dope as prepared above is prefiltered through a 200-mesh stainless steel screen to remove excess LiCO powder. Approximately 300 g. of the dope are then placed in aspinning cell, then filtered through a sand and screen filter packbefore reaching the spinneret. The spinneret has holes, each having adiameter of 0.003 inch (0.076 mm.). They are arranged in three circleswithin a half-inch (1.27 cm.) diameter overall. The spinneret jets intoa 65C. bath of distilled water which is continuously recirculated andfiltered. The bathis also, continuously diluted with fresh water toprevent excessive build-up of salt and solvent in the bath. The yarn isdrawn through a 135 cm. bath and over a 3.75 inch (9.53 cm.) diameterbobbin and wound up on a second 3.75 inch (9.53 cm.) bobbin. The spinstretch is controlled by varying the wind-up speed of the first bobbin.The minimum wind-up speed possible without yarn build-up in the bath is32 ft./min. or 384 in./min. 16.26 cm./sec.). The calculated unextractedpolymer solution jet velocity is 605 in./min. (25.61 cm./sec.). Thisindicates a lengthwise extraction shrinkage of 36.5% before wind-up. Theoptimum wind-up speed is found to be 540 in./min. (22.86 cm./sec.) andthe maximum wind-up speed at which continuous spinning was possible was635 in./min. (26.88 cm./sec.). These values correspond to spin stretchvalues of 1.4 and 1.65, respectively, based on the normalized value of384 in. min. (16.26 cm./sec.) at spin stretch of 1.0. Based on jetvelocity they are 0.893 and 1.05, respectively.

The as-spun yarn is soaked for 2 hours in water, then allowed to dry onthe bobbins. The as-spun yarn has an orientation angle of 27 asdetermined by X-ray analysis. T/E/Mi/Den values for the as-spun yarn are5.9/4.8/354/3.l (after boil-off).

The yarn is subsequently heat treated by drawing it over a 12-inch (0.03m.) long grooved hot shoe at 30 ft./min. (15.24 cm./sec.) to give a 2second contact time. A nitrogen blanket is maintained over the hot zone.

The wet-spun sample after various heat treatments has the followingproperties (boiled-off):

This example illustrates the effect of heat treatment on the tenacityand modulus of fibers of poly(1,4- benzamide) and preparation of alaminate from such fibers.

A 2-liter resin-making kettle is dried by flaming and allowing to coolin a nitrogen atmosphere. The kettle is fitted with an egg-beater-typealluminum stirrer and nitrogen inlet and outlet devices. While a slowcurrent of dry nitrogen is passed through the kettle, it is charged with150 g. of p-aminobenzoyl chloride hydrochloride. To this are addedrapidily with vigouous stirring, 770 ml. of TMU, precooled to about -lC.(This solvent had previously been dried to a water content of less than150 parts per million by distillation over calcium hydride).Considerable heat is evolved initially; this is absorbed by surroundingthe kettle with an icebath for the intital minutes after reaction wasstarted. After stirring the kettles contents for about 2 hours at about21C., 38.0 g. of powdered, anhydrous lithium hydroxide is added and thestirred mixture is raised to a temperature of 120C. by external heating.The highly viscous, rubbery mixture becomes a more free-flowing spindope as stirring at 120C. is continued for about 30 minutes. Bydistilling off about 50 ml. of solvent under a vacuum of about cm. ofmercury, most of the water, introduced by reaction of lithium hydroxide,is removed. The spin dope contains 10.2% polymer content.

Approximately 5 g. of spin dope are added to 200 ml.

water in a Waring blender. After stirring this for 5 minrated polymer. Afurther 200 ml. water are added and stirring continued for a further 5minutes. The treatment is repeated, using 200 ml. ethanol in place ofthe water. The polymer is filtered and dried for 15 hours at -80C. in avacuum oven (20 -40 cm. of mercury) fitted with a nitrogen bleed. Thepolymer has an inherent viscosity of 1.38, a peak height ration of 0.76,and, under the conditions of the sedimentation test. leaves no polymericresidue on the bottom of the test tube after 48 hours.

Spinning: The above spin dope is dry spun as follows. From the spinningvessel, in which it was kept at 155C, the dope is expressed by a pistonunder a pressure of 68 lb./in. (4,780 g./cm. through a spinneret adapter(at C), then through a spinneret (at 160C.) The spinneret is of theprotrusion type, consisting of nine effective holes, each of 0.004 in.(0.01 cm.) diameter. In the adapter the dope passes through a filterconsisting of one 50 mesh screen, three 200 mesh screens, one cottoncloth of 2.4 oz./yd. (81.5 g./m. woven in a plain weave with 148 picsper inch and 160 ends per inch, and one table felt pad of 2.8 oz.- /yd.(95 g./m. and a density of 7.8 lbs/ft. (0.125 g./cm. at atmosphericpressure. The dope jets through the spinneret at a rate of 2.92 ml./min.into a cocurrent stream of nitrogen at a temperature of 235C., flowingat 5 it /min. (0.142 m. /min.), in a spinning cell with walls heated at200C. The fibers issuing from the cell are passed through water andwound up at a rate of yd./min. (123.5 m./min.), (spin stretch factor is3.2 The fiber is wound up at this rate for 1 hour. The yarn cake is thenimmersed in a large excess of distilled water at 21C. for 15 hours toextract salt and solvent. The wet cake is stored in a polyethylene bag.The as-spun and extracted yarn exhibits T/E/Mi/Den. 8.22/3.1/509/3.06,after being dried.

Extracted and dried yarn of the preceding preparation is passed througha hot stainless steel tube, 0.286 inch (7.26 mm.) inside diameter and 32inches (81.3 cm.) in length, at 12 ft./min. (3.66 m./min.) under anitrogen atmosphere without significantly changing its length. Thenitrogen is passed through the tube from the yarn entry end at such arate as to change the atmosphere in the tube once every minute. The tubeis heated externally by a 12 inch (0.3 m.) long furnace which wascontrolled by a thermocouple braised to the external central surface ofthe pipe and connected to a Minneapolis-Honeywell Pyrovane controller.The nominal heat-treating temperature of the tube given in Table 111 isthe temperature indicated by a thermocouple braised to the center of theinside of the tube. A profile of the temperature in the tube for anominal temperature of 536C. obtained by varying the position of a testthermocouple is given in Table 11.

TABLE 11 TEMPERATURE PROFILE OF HEAT-TREATING TUBE Distance fromEntrance 1n. (Multiply X 2.54 for distance in cm.) Temperature, C.

TABLE ll-Continued TEMPERATURE PROFILE OF HEAT-TREATING TUBE flangerests upon shims which are sized to leave a gap of 0.1 in. (0.254 cm.)between the plug and the bottom surface of the mold. The mold and itscontents are pisim c?t fr; n E. |it r i}t-e placed in a Pasadena press,the platens of which have g f g Temperature Q been heated to 150C. Thepress is closed and a total 17 536 pressure of 1.5 tons (1.36 metrictons) is applied to the 13 537 mold. The mold is left in the press for2.75 hr. before 39 being taken out and cooled to room temperature. 55The ends of the laminate sample are cut off and hand 221 213 sanded. Thesample measures 5.32 X 0.502 X 0.095 in. 32 184 (13.5 X 1.27 X 0.24cm.), The tangent modulus of elasticity in flexure (i.e., flex modulus)of the sample is Properties of yarns treated at different temperaturesmeasured having a 4 in. (10.16 cm.) long portion are given in Table ill.chosen in the middle of the laminate as the test section.

TABLE 111 Nominal Heat Trent. Fiber Fiber Orient. Peak Temp. Den. Ten.Elong. Mod. Den. lnh Angle Height Sample "C Fil. g/tl g/tl g/c1n.3 VisRatio 1 Room 3.060 8.22 3.1 509 141x 1.67 18 .63

Temp.

Preparation of a Laminate: Yarn from the preceding The sample is mountedas a supported beam with load spin is heat-treated by passing the yarnthrough a hot applied in the center in an lnstron testing machine. tubeat a nominal temperature of 536C. and a speed The load member isdeflected at the rate of 0.02 in./- of 11.58 ft./min. (3.53 m./min.). Itis wound up on a min. (0.508 mm./min.) until a load of 20 lb. (9.07 kg.)bobbin of 4.13 in. (10.5 cm.) diameter as a thin cake 40 is applied. Theflex modulus is found to be 14.41 X 10 approximately 1.5 in. (3.81 cm.)wide. The traversing lb./in. (10.13 X 10 g./cm. By comparison,commerrate at the wind-up is 1 stroke/11 revolutions; the yarn cialaluminum with a modulus of 10 to 20 X 10 filaments in the cake arenearly parallel. A test specilb./in. (70.3 to 140.6 X 10 g./cm. has adensity of men of the yarn has Denier/T/E/Mi values of 2.56 g./cm.Laminates ofE glass have a theoretical 2,967 16.17 1 7 1096 moduluslimit of 8 x 10 lb./in. (56.2 X 10 g./cm.'-") at A laminate is preparedfrom the above fiber as fola density of 2.22 g./cm. lows. A mixtureconsisting of 10 g. Epon 815 (Shells epoxy resin), 9 g. or Nadic (methylanhydride curing EXAMPLE V agent Allied Chemical Corporation), and 0.1g. of benzyldimethylamine is poured into a mold having a cavity PolymerPreparation: A 250-ml. round-bottomed with the following dimensions:length, 5.95 in.; width, fl sk q pp i h a stirrer, ni r g n inlet tube.n 5 i d h, ()9 i (152 x 1 27 x 2,29 Th calcium chloride drying tube isflamed with a Bunsen mold and its contents are placed in a vacuumchamber bruner and simultaneously flushed with nitrogen. The for 1 hourto remove gases. The mold is then removed y flask with its attachmentsis Placed in a y' and from the vacuum chamber. The fiber is cut from the11-52 gof P-aminobenzoyl Chloride hydrochloride is bobbin and dividedinto ribbons 5.95 in. (15.2 cm.) add The flas s then tta d to a ng motorlong) hi h are arranged i a stack i h h fib band nitrogen source andstirring and slow nitrogen flow stantially parallel to the long axis tothe ribbon. The started while the flask is cooled in an ice bath. Coldfiber weighs 4.84 g. The fiber is placed on top of the TMU (58.7 ml.) isadded quickly in a single portion. resin and gently pressed in, carebeing taken to pre- The monomer immediately dissolves andpolymerizaserve the parallel orientation of the fibers. The mold tionstarts. Stirring is continued for 2 hours with ice and its contents arereturned to the vacuum chamber cooling and for 2 hours without cooling.The forming for a further 30 minutes for removal of unwanted polymeryields a viscous, somewhat hazy dope. Polygases. The mold is then takenfrom the vacuum chammer is isolated from a sample of the dope at 4 hoursby her and a flanged plug, having dimensions of 5.75 X 0.5 precipitationin water and is found to have an inherent X 1.0 in. t 14.6 X 1.27 X 2.54cm.), is pushed into the cavity and pressed slowly down upon theresin-fiber mix in order to allow bubbles and excess resin to find theirway to the open spaces between the plug ends and viscosity of 1.38.

Fiber Preparation: A sample of polymer dope, prepared as described abovebut from a duplicate reaction mixture, is charged into a l5-ml.,syringe-type cell havstructed of stainless steel. A -hole spinneret,having 0.003 in. (0.076 mm.) holes and constructed of a platinum alloy,is attached to the syringe by a ring-nut over a simple filter packconsisting of a 200-mesh stainless steel screen, a thin layer of fineglass wool and then 50- mesh, 200-mesh, and 50-mesh screens insuccession. The dope is extruded at a slow rate into a water bath keptat about 50C. and the fibers are collected on a bobbin at a speed of 61ft./ min. (18.6 m./min.) after traveling in the bath for about 3 ft.(0.91 m.). The fibers have the following properties:

The polymer of the as-spun fiber has an ninh of 1.12 and a peak heightratio of 0.78.

Some of the dopes used in this invention may be further characterized bytheir microscopic birefringent qualities which are manifested by theireffect on planepolarized light. Such an observation may be made by thefollowing method. A drop taken from the interior of a dope sample ofthis invention. is put on a dry, clean strain-free glass slide; a squarecover of glass, sup ported on one edge by a glass tube or wire of knownthickness (1.3 mm. diameter is convenient) is pressed down on the dropso as to form the roof of a liquid wedge. The edges are sealed with afast-drying binder avoiding actual contact with the dope. The sharp edgeof the wedge is sealed by excess dope which is squeezed out. In theoperation, common care should be taken to avoid evaporation, moistureuptake, excessive shearing actions, dirt, and any suspended solidparticles.

The wedge is positioned in a light beam, on a micro scope stage betweencrossed polarizer and analyzer, so that the thickness of the center ofthe layer of dope through which the light beam passes is 80;.t inthickness. The intensity is measured with polarizer and analyzer crossed(1 (superscript s to denote sample present in wedge) and with analyzerremoved (L and the difference I L, is obtained. The transmitted lightmay be measured by conventional light sensitive detectors (e.g. by photomiltipliers, selenium or cadmium light meters, bolometers, etc.). Thesame measurements are then made on a similarly constructed wedgecontaining air, and the difference L" I (superscript c for control) isrecorded. When these dopes of this invention are placed in the wedge,the expression (If I (I 31 1 will be greater than zero, and greater thancan be accounted for by experimental error. It represents the increasein light transmittance through the analyzer due to the presence of thesample. The magnitude of (If 1 -(l 1 will vary with the solvent beingused, polymer concentration, and concentration of dissolved salt, andthe units in which light intensity is measured.

EXAMPLE VI The results presented in the following Table V illustrate theeffects of using various chain terminators, with and without addedlithium hydroxide monohy- 16 drate, in preparing the po1y(p-benzamide)used in this invention. Data for two control runs are also presented. Ineach of these polymerizations, 200 ml. of TMU are placed in anice-cooled glass reaction vessel and 0.0025 mole of the designatedterminator is added thereto. To these ingredients are added 32 g. (0.17mole) of paminobenzoyl chloride hydrochloride. The contents of thereaction vessel are stirred for 15 minutes, after which the cooling bathis removed and the contents stirred for another 1.75 hour. Lithiumhydroxide monohydrate 12.8 g., 0.31 mole) is added to the vessel and thecontents are stirred for 30-60 minutes at autogenous temperature. Thereaction mixture is then permitted to stand for 20 hours at autogenoustemperature before being agitated with water in a blender to precipitatethe polymer. The latter is collected, washed three times with water andonce with 28 alchol (all done in a blender), and dried in a vacuum oven.The particular terminator employed, the polymers viscosity, and pres-*Added 1 hr. after monomer addition instead of 2 hr. later.

EXAMPLE VII This example illustrates that some dopes used in thisinvention cause an increase in the transmittance of light throughcrossed polarizers.

In this example, the apparatus by which the anisotropic character ofthese dopes is determined consists essentially of an A. 0. SpencerOrthoscope llluminator which contains a tungsten overvoltage microscopelamp (color temperature 3800K.), an optical wedge containing the sample,an optical wedge containing air, a Bausch and Lomb Polarizing Microscopehaving a Leitz 10X objective and a Leitz 10X ocular Peripian, a PolaroidM 3 Industrial Land Camera and a Gossen Sinarsix exposure meter. Thewedge containing the sample is prepared as previously described and ispositioned on the microscope stage (i.e., between the polarizer and theanalyzer) to provide a sample layer of 80,u.thickness in the path of anylight which reaches the analyzer and the light meter. The polarizer andthe analyzer are adjusted to provide 90 crossed polarization planes.Light from the lamp which passes the analyzer by the route previouslydescribed is projected into the.

camera and is measured in the image plane (at the ground glass level) bythe exposure meter (1 The same measurement is made with the analyzerremoved (L This is repeated with the control wedge of air M. thick togive 1 and L The light readings from the Sinarsix exposure meter may beconverted to light intensities by multiplying them by 0.301 (i.e. by log2) and then determining the antilog of this product. These I I valuesare designated IQ" l3" 1 and L" Y v The expression l,.' /l is the ratioof light intensities transmitted by the dope being examined. The ratio I/I is the ratio of light transmitted by the control wedge. Thedifference (lfi' /l (L,""

/l represents the increase in intensity of light transmitted due to thepresence in the wedge of the dope being examined.

Since the theoretical maximum value of 13" /l I," /I 0.5 an index of theincrease of light transmittance may be conveniently taken asv 2(l /l IL"X 100 since in this way,

End Uses: The fibers are excellent for reinforced plastic laminatesbecause of their high modulus. low density. high dimensional stability,high strength, high thermal stability and high flexural rigidity at agiven laminate weight. Specific end-uses mayinclude spiral 18 I TABLE VILIGHT DEPOLARlZATlON BY POLY(p-BENZAMIDE Poly( p-benzamide weightPercent In Dope ninh Wgt. 71 Salt wound pressure vessels, skis, bows,fishing rods, and

golf club shafts.

The high modulus, high strength, fatigue resistance I and impactstrength of the fibers render them useful in mechanicalrubber goods suchas belts.

The fibers are useful in sewing thread. and in uses such as protectiveclothing, laundry press covers, filtration fabrics, industrial hose,dryer felts, all of which utilize the high thermal stability of thefiber.

What is claimed is:

1. A method for increasing the initial modulus and reducing theorientation angle of undrawn fibers consisting essentially ofpoly(p-benzamide having an orientation angle of up to about 55comprising heating the undrawn fibers at a temperature of at least 350C.

While under tension or, while relaxed.

1. A METHOD FOR INCREASING THE INITIAL MODULUS AND READUCING THEORIENTATION ANGLE OF UNDRAWN FIBERS CONSISTING ESSENTIALLY OFPOLY(P-BENZAMIDE HAVING AN ORIENTATION ANGLE OF UP TO ABOUT 55*COMPRISING HEATING THE UNDRAWN FIBERS AT A TEMPERATURE OF AT LEAST350*C. WHILE UNDER TENSION OR, WHILE RELAXED.